1. Field of the Invention
The present invention generally relates to a woven fabric which is designed for use in a papermaking, cellulose or board manufacturing machine and which along each end has a plurality of loops to be included in a loop seam to form an endless woven fabric.
2. Description of the Prior Art
As will be known to those skilled in the art, papermaking machines generally include three sections which are generally referred to as the formation, press and dryer sections. The present invention finds particular application in papermaker's felts which are employed in the press section of a papermaking machine.
Typically, such felts include a supporting base, and a paper carrying or supporting layer fixed to the base. Frequently, the base fabric is a woven fabric which is used as an endless belt. The woven fabric may be woven as an endless loop and utilized as such so there is no seam or, alternatively, the fabric may be woven to have two ends which are joined at a seam to form the endless loop. Various seams are known in the art, including pin type seams which utilize a joining wire or pintle which is inserted through seam loops at each end of the fabric to render it endless.
One technique of forming a fabric having seam loops is to provide an endless weave wherein loops are formed by weaving stacked weft yarns around a forming wire, as shown in U.S. Pat. No. 3,815,645. A common problem associated with this type of loop formation is non-uniform loop alignment, both in the vertical and horizontal axis, when the forming wire is removed. The misalignment creates a seam that is difficult to mesh.
FIGS. 1-3 show representative loop misalignments experienced in common prior art endless woven seams. Generally, as a loom weaves the loops in an endless weave, it naturally offsets the returning weft position slightly from its outgoing weft position. Therefore, it is necessary to maintain the weft yarns in a stacked relationship throughout the fabric through the balanced weave of the warp yarns. The last warp yarn, however, is generally not balanced by adjacent yarns on each side and therefore, an unbalanced crimp force is applied to the weft yarns in the loop area, as shown by the arrows in FIG. 2. As a result, the two weft yarn passes which form each loop are not balanced by warps and the loops tend to be misaligned.
Another problem associated with standard seams is that the seam area has a yarn density twice that of the body since each meshed seam half has a density similar to the body.
Accordingly, it is desired to provide a base fabric having seam loops which are easier to intermesh and more uniform fabric characteristics in the seam area.